1. Field of the Invention
The present invention relates to a method of manufacturing a monolithic stationary phase, and more particularly, to a method of manufacturing a polymer-based monolithic stationary phase in an ionic liquid reaction medium via microwave-assisted vinylization and polymerization, as well as the monolithic stationary phase produced thereby.
2. Description of the Prior Art
Monolithic columns including organic polymer- and silica-based monoliths have been demonstrated to be a very good alternative to particle-packed columns for highly efficient separations in capillary electrochromatography (CEC) and HPLC because their small-sized skeletons and large through-pores can simultaneously reduce the diffusion path length and flow resistance. Several advantages such as low consumption in the sample and mobile phase, limited peak broadening, and good compatibility with mass spectrometric detection also promote the general acceptance of monolithic technology. Moreover, the use of monolithic materials as an attractive alternative in immobilized enzyme reactors (e.g. microreactors) that provide the advantages of low back pressure, high mass transfer, and reduction of the reaction time from several hours to a few minutes, are now finding fast acceptance in various areas such as protein digestion in proteomics, chemical syntheses, and the pharmaceutical industry. Organic polymer monoliths consisting of acrylamide-, methacrylate ester-, and styrenebased polymers have been successfully used as chromatographic stationary phases and immobilized microreactors, however, their preparation including column vinylization and monolith syntheses are often time-consuming (i.e. 3 to 24 hours for vinylization and 15 to 24 hours for monolith synthesis using thermal heating).
Room temperature ionic liquids (RTILs) are salts with melting points below 100 C. In addition to showing valuable properties such as high thermal and chemical stability, and being liquids at ambient temperature, they are considered as promising solvents for green processes because of their negligible vapor pressure. While ILs are already applied in various chemical syntheses, and can lead to significant improvements in the rate and yield of reactions, there have been intensive studies into radical polymerization in ILs recently (See, for example, J. Lua, F. Yana and J. Texter, Prog. Polym. Sci., 2009, 34, 431). It is also suggested that free radical polymerization in ILs results in considerably faster reaction rates and yields, and higher molecular weight than in common solvents. In the presence of ILs as reaction solvents, complete conversion of monomers such as methyl methacrylate or styrene to polymer was achieved within a few hours, but with conventional solvents more time is often required. This is likely due to the increased polarity of the IL medium that improves propagation rate while its increased viscosity reduces the termination rate in polymerization. These influences on chain-termination processes led to high molecular weight products and rapid reaction rates.
Rapid synthesis by microwaves has attracted considerable attention in recent years. One of the most valuable advantages of using microwave heating for chemical synthesis is the dramatic reduction in reaction time since microwave irradiation produces efficient internal heating by direct coupling of microwave energy with the molecules that are present in the reaction mixture. In comparison with reactions under conventional thermal methods such as using oil baths or hot plates, microwave heating is also able to reduce side reactions, increase yields, and improve reproducibility. Studies on microwave-enhanced chemistry have shown that the efficiency of the interaction of molecules in a reaction mixture (substrates, catalyst and solvents) with electromagnetic waves (named “microwave dielectric effect”), mainly depends on the polarity of the reaction mixture. ILs contain anion-cation pairs and therefore have a relatively high density of strong dipoles, which make them promising candidates for microwave absorption. With this, the use of ILs as reaction media in microwave-assisted polymer synthesis has been reported recently. Regarded as green solvents, the use of ILs would contribute to the depletion of volatile organic compounds (VOCs) emission as well as in energy savings (L. Liao, C. Zhang and S. Gong, J. Polym. Sci., Part A: Polym. Chem., 2007, 45, 5857).
To date, no report has been published addressing the feasibility of ILs in the in situ syntheses of organic polymer-based monolith materials which show high potential for chromatographic stationary phases and microreactors in proteomics and chemical syntheses.